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Many of you have helped with my short lived 4-53 blower on a Y block project, Thanks.
I have found out that a 4-53 is too small for for a 292, would be better for a 239 flathead but too small for me. (Anyone want to buy a 4-53 cheap?) It is the larger one of the two.
This brings us to my new project, a 4-71 blower on a Y block. Before I get too far into this, what are the pros and cons?
Price, I can make most of the parts I will need and a Hamber is getting me a good deal on some stuff.
Performance, well, I guess that will be a plus.
Dependability, any thought on this?
Will affect the idle quality? I have an automatic.
What about some thoughts on how to set it up, What size carb should I run? would like to use a 4150 Holley.
How about the power valve? I guess that works the same. What about my vacuum advance? can I still use it?
Anything else I should consider for a street 292 Y block in a Model A?

Member

Compression ratio plays a large part in setting one up. What is typical CR for Y block, if close to 9:1 it limits you how much boost you can generate. Can you get dished pi$tons for Y block? 4150 carbs will need to be boost reverenced for blower setup.

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One big misunderstanding/lack of understanding on cam choice...
A cam with 112 to 114 degree (intake to exhaust) lobe centers is one criteria to have when you pick a cam. If you pick a cam with the more normal 110 or less degrees, will let the blower pressure just go out the tail pipe rather than push the pistons down the bores..!
A cam for a carbureted engine is different than a cam with a blower (belt driven).

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You should get plenty of good information here on the HAMB on this, if you need more, I did a Google search for you, when you click on a picture it takes you to the text from which the photo came from.

Member

4X71 =284 cubic inches you have 292.
You can overdrive the blower to make up for the differance. On a street motor for relialibity I would run 3 to 5 pounds of boots. Things like double keyway the harmonic balancer and make sure your blower is parallel to the crank or you will through belts. It's not rocket science but takes a well thought out plan.
Good luck
Terry aka dirt t

Member

The more parts and systems you put on an engine, the more failure points it has. If you simply want reliable performance there should be plenty of conventional N/A tuning possible. If you want a blower for the sake of having a blower motor, that's going to be a different road to walk, quite possibly with a less reliable engine as a result.

Member

4X71 =284 cubic inches you have 292. You can overdrive the blower to make up for the differance"

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Thats somewhat misleading, because that 292 will need two revolutions to use its 292 ingested cubic inches, while that 280 inch displacement blower (4-71) will be pushing in a total 560 cubic inches during two revs, if run at 1:1 ratio and you let it eat (open throttle). No overdrive required, that's how you make boost.

Member

Compression ratio plays a large part in setting one up. What is typical CR for Y block, if close to 9:1 it limits you how much boost you can generate. Can you get dished pi$tons for Y block? 4150 carbs will need to be boost reverenced for blower setup.

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I have two sets of heads, one set that will give me about 9:1 and another one 8.1 :1 or so. The higher compression heads have the larger valves. I would like to be about 4 to 5 lbs of boost if that would not hurt dependability much.
What would have to be done to "boost reference" the carb?

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Yes, I have been reading about that. I have a larger rumpity cam in the car now I think it is 108* but would have to check. This may end up the most expensive single item to correct, what would you think about a stock cam? I don't know the the separation angle is on it.

Member

Blowers produce heat!
That's the only drawback I have to list.
Power all the time is the biggest plus. Boost referenced power valve is a must.

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The heat thing is a down side, I drive this in the summer and would hate to worry about overheating all the time, how bad is this problem with 4 to 5 lbs of boost?
Explain about the boost referenced power valve.

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In street mode, I'm producing 6 pounds of boost.(turbo guys laugh now). By 3000 rpm, it's producing over 400hp and rising. Twin fans, big radiator.
Temps climb at highway speed, sustained 3000+ rpm makes the temp climb toward 200. Not enough to worry about, but it freaks me out to see it rise.
Ever hear a blown car ''surge''? If the power valves don't "see'' boost they are experiencing constant vacuum and the engine searches for equilibrium. At idle, it will continuously rev then drop, not something I'd want to drive, with a clutch.

Member

My blown flathead Ford takes some fuel to get it started, and I had to play with power valves on the Strombergs a bit. It runs hot but it ran hot before..

My stock SBC daily got a street blower earlier this year. It fires right up without pumping the gas and never runs hot. I just plopped the Q-jet back on without any changes, no idea what it has for a power valve.

Both don't see more than 5psi, but that seems enough to make a big difference, although a good running Prius would probably outrun either one.

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Here is a chart for compression ratio efficiency. Ideal is 12:1 or under "effective comp ratio" not static. Static CR is on the far left of the column. If you use 8:1 static, and 6 lb boost you would be at 11.3 effective CR. So, using 5-6 lb of boost would be your sweet spot. You will have to ask a carb guy about boost reference, but I know if those huffers cough and back fire it blows powervalves out. I would look into running the heads with larger valves, only if you can find dish pistons to lower CR. Cams; some came with 114 lobe seperation. The old GM 350hp cam "151" was 114, so there are some stock cams but dont know squat about Y blocks. Also, look for a cam with split duration, a bit more duration on the exhaust side. No problem with air being forced into the engine, but longer duration on exhaust will help flow for exhause getting out.